Line Spectrum Pairs (LSP) parameters, also referred to as Line Spectral Frequencies (LSF) parameters, are used to characterize audio signals. Generally, a frame of audio signals may be described with a group of LSP parameters. Each group of the LSP parameters includes multiple pieces of data that are between 0 and π (the ratio of the circumference of a circle to its diameter). The number of pieces of data included in the group of LSP parameters is referred to as an order of the LSP parameters. To process the audio data using the LSP parameters, usually, the LSP parameters are first converted to Linear Prediction Coefficients (LPC) parameters, and then the LPC parameters are converted to audio signals using an LPC synthesizer.
In order to improve the tone of the audio signals, the peaks of the spectrum (formants) are enhanced, for example using the following two methods. A first method is an empirical formula adjustment based on LSP parameters. A second method is an adjustment based on LPC parameters, where the LSP parameters are converted to the LPC parameters and a post-filter is constructed by adjusting the LPC parameters, so as to enhance the formants. However, the foregoing methods have the following defects. Defects of the first method include that the formants are not sufficiently enhanced, which cannot effectively improve the tone. Defect of the second method is that frequency tilt is easily caused, an adjustment cannot be made based on a frequency band, and a large workload on the computations is required for this method. Therefore, it is desirable to have more efficient method and device for the audio signal processing.